Nickel base alloy

ABSTRACT

A nickel base alloy consisting essentially of, in weight percent, up to 0.18% carbon, from 14.2 to 20% cobalt, from 13.7 to 16% chromium, from 3.8 to 5.5% molybdenum, from 2.75 to 3.75% titanium, from 3.75 to 4.75% aluminum, up to 4% iron, from 0.005 to 0.035% boron, up to 0.5% zirconium, up to 0.5% hafnium, up to 0.75% columbium, up to 0.5% rhenium, up to 0.75% tantalum, up to 1.0% manganese, up to 3% tungsten, up to 0.5% rare earth metals, balance essentially nickel with incidental impurities and having a morphology comprised of gamma prime particles which consist essentially of randomly dispersed irregularly shaped particles less than about 0.35 micron. A method of treating an alloy consisting essentially of, in weight percent, up to 0.18% carbon, from 14.2 to 20% cobalt, from 13.7 to 16% chromium, from 3.8 to 5.5% molybdenum, from 2.75 to 3.75% titanium, from 3.75 to 4.75% aluminum, up to 4% iron, from 0.005 to 0.035% boron, up to 0.5% zirconium, up to 0.5% hafnium, up to 0.75% columbium, up to 0.5% rhenium, up to 0.75% tantalum, up to 1.0% manganese, up to 3% tungsten, up to 0.5% rare earth metals, balance essentially nickel with incidental impurities, to develop a morphology comprised of gamma prime particles which consist essentially of randomly dispersed irregularly shaped particles less than about 0.35 micron in diameter. It comprises the steps of heating the alloy at a temperature of at least about 2,000* F., cooling the alloy and heating the alloy at a temperature of from about 1,500* F. to about 1,850* F.

[151 3,653,987 Apr. 4, 1972 United States Patent Boesch m m w e N n M a U M Y b C O m k m m m A Y w E N 1 k Ammmm BWS m n.-

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[21] Appl. No.: 42,412

domly dispersed irregularly shaped particles less than about 0.35 micron.

' A method of treating an alloy consisting essentially of, in weight percent, up to 0.18% carbon, from 14.2 to 20% cobalt, from 13.7 to 16% chromium, from 3.8 to 5.5% molybdenum, from 2.75 to 3.75% titanium, from 3.75 to 4.75% aluminum, up to 4% iron, from 0.005 to 0.035% boron, up to 0.5% zir- 0 0 2H7U 31 8 5 2 7 1 1' ,C2 1:0 7 l n i N m2 m3 m m2 1 "3 8 "on 4 4 1 mh c 0r am L mi 0 W d td .I UhF 11]] 2 8 555 [ii References Cited UNITED STATES PATENTS 3,536,542 10/1970 Murphy et al.

conium, up to 0.5% hafnium, up to 0.75% columbium, up to 0.5% rhenium, up to 0.75% tantalum, up to 1.0% manganese,

mmmuwmxlmz up to 3% tungsten, up to 0.5% rare earth metals, balance essentially nickel with incidental impurities, to develop a morphology comprised of gamma prime particles which con- Primary Examiner- Richard 0. Dean sist essentially of randomly dispersed irregularly shaped parti- Attorney--Richard A. Speer, Vincent G. Gioia, Howard R.

Berkenstock and Robert Dmpkin cles less than about 0.35 micron in diameter. It comprises the steps of heating the alloy at a temperature of at least about 57] ABSTRACT 2,000 F., cooling the alloy and heating the alloy at a temperature of from about 1,500 F. to about 1,850 F.

A nickel base alloy consisting essentially o f, in weight percent, up to 0.18% carbon, from 14.2 to 20% cobalt, from 13.7 to 7 Claims, 5 Drawing Figures Patented April 4, 1972 S Sheets-Sheet l \ESQE walk mm QR Db NO/J 79/0/073 1N33U3d lmvsmfon. WILLIAM J. 50530 AHarney Patented April 4, 1972 5 Sheets-Sheet 2 FIG. 2.

FIG. 3.

INVENTOR. WILL/AM J. BOESC/l M? Attorney Patented April 4; 1972 3 Sheets-Sheet 5 FIG. 4.

mvs/vro/v. WILL/AM .1. BOESCH A Horney NICKEL BASE ALLOY The present invention relates to a nickel base alloy and more particularly to a nickel base alloy with improved high temperature properties. It further relates to a method of treating a nickel base alloy and more particularly to a method of treating a nickel base alloy so as to improve the alloys high temperature properties.

Nickel base alloys have been known and used at elevated temperatures for quite some time. In particular, it is known that nickel base alloys can be markedly improved by employing a precipitation hardening mechanism so that their useful life is not only prolonged, but the alloy can be used at higher temperatures. Perhaps the best known strengthening precipitate in nickel base alloys is the intermetallic compound known as gamma prime. Gamma prime is believed to have the general composition M (Al, Ti). As used herein, the M portion of the gamma prime composition is regarded as consisting mainly of nickel with some substitution of chromium and molybdenum and is considered to have the approximate atomic proportions, 95 nickel, 3 chromium, and 2 molybdenum.

, I have found that the already good high temperature properties of nickel base alloys consisting essentially of, in weight percent, up to 0.18% carbon, from 14.2 to cobalt, from 13.7 to 16% chromium, from 3.8 to 5.5% molybdenum, from 2.75 to 3.75 titanium, from 3.75 to 4.75% aluminum, up to 4% iron, from 0.005 to 0.035% boron, up to 0.5% zirconium, up to 0.5% hafnium up to 0.75% columbium, up to 0.5% rhenium, up to 0.75% tantalum, up to 1.0% manganese, up to 3% tungsten, up to 0.5% rare earth metals; e.g. cerium and/or yttrium and/or lanthanum, balance essentially nickel with incidental impurities, can be materially improved if the alloys are treated to develop a particular gamma prime morphology. This particular morphology is comprised of gamma prime particles which consist essentially of randomly dispersed irregularly shaped particles less than about 0.35 micron in diameter.

1n the past nickel base alloys having the composition described in the preceding paragraph often had a morphology comprised of oriented cubic gamma prime particles about 0.5 micron per side. These cubic gamma prime particles adversely affected the alloys high temperature properties as they tended to agglomerate during prolonged elevated temperature service and form rod-like particles in certain crystallographic planes along which slip rapidly occurs. Formation of these cubic gamma prime particles was due to the high temperatures employed during the second stage of the prior art heat treatments, during which gamma prime precipitation is initiated. The method of the present invention avoids the formation of cubic gamma prime by employing a maximum second stage temperature of 1,850 F. A particular prior art heat treatment used a second stage temperature of 1,975 F. It comprised the steps of: (l) heating at a temperature of 2,l35 F. for 4 hours and cooling; (2) heating at a temperature of 1,975F. for 4 hours and cooling; (3) heating at a temperature of 1,550" F. of for hours and cooling; and (4) heating at a temperature of 1,400 F. for 16 hours and cooling.

It is accordingly an object of this invention to provide a nickel base alloy with improved high temperature properties.

It is a further object of this invention to provide a method of treating a nickel base alloy so as to improve the alloys high temperature properties.

The foregoing and other objects of the invention will be best understood from the following description, reference being had to the accompanying drawing and photomicrographs wherein:

FIG. 1 is a plot of percent elongation versus time for two samples of a nickel base alloy which underwent different second stage heat treatments at 1,975 F. for 4 hours and at 1,700" F. for 8 hours;

FIG. 2 is a photomicrograph at 7,200X of a nickel base alloy which underwent a second stage heat treatment at l,975 F. for 4 hours;

FIG. 3 is a photomicrograph at 7,200X of a nickel base alloy which underwent a second stage heat treatment at 1,700" F. for 8 hours;

FIG. 4 is a photomicrograph at 7,200X of a nickel base alloy which underwent a second stage heat treatment at l,750 F. for 8 hours; and

FIG. 5 is a photomicrograph at 7,200X of a nickel base alloy which underwent a second stage heat treatment at 1,750 F. for 24 hours.

The alloys of the present invention have a composition consisting essentially of, in weight percent, up to 0.18% carbon, from 14.2 to 20% cobalt, from 13.7 to 16% chromium, from 3.8 to 5.5% molybdenum, from 2.75 to 3.75% titanium, from 3.75 to 4.75% aluminum, up to 4% iron, from 0.005 to 0.035% boron, up to 0.5% zirconium, up to 0.5% hafnium, up to 0.75% columbium, up to 0.5% rhenium, up to 0.75% tantalum, up to 1.0% manganese, up to 3% tungsten, up to 0.5% rare earth metals; e.g., cerium and/or yttrium and/or lanthanum, balance essentially nickel with incidental impurities and a morphology comprised of gamma prime particles which consist essentially of randomly dispersed irregularly shaped particles less than about 0.35 :micron, preferably 0.25

micron, indiameter. In addition the: alloys can have other precipitates such as an M C precipitate (M is generally chromium which improves grain boundary ductility. Alloys are respectively considered to be within the scope of the invention and within the preferred embodiment of the invention even if they have occasional gamma prime particles (gamma prime particles which constitute less than five volume percent) in excess of 0.35 and 0.25 micron. In most instances, the gamma prime particles of the preferred embodiment range between 0.1 and 0.25 micron.

To illustrate the nickel base alloy of the present invention, reference is directed to Table I which describes specific ranges for nickel base alloys of the present invention.

The method of the present invention comprises a two and preferably three stage heat treatment, i.e., two or three beatings each followed by cooling, applied to alloys consisting essentially of, in weight percent, up to 0.18% carbon, from 14.2 to 20% cobalt, from 13.7 to 16% chromium from 3.8 to 5.5% molybdenum, from 2.75 to 3.75% titanium, from 3.75 to 4.75% aluminum, up to 4% iron, from 0.005 to 0.035% boron, up to 0.5% zirconium, up to 0.5% hafnium, up to 0.75% columbium, up to 0.5% rhenium, up to 0.75% tantalum, up to 1.0% manganese, up to 3% tungsten, up to 0.5% rare earth metals; e.g., cerium and/or yttrium and/or lanthanum, balance essentially nickel with incidental impurities. The treatment develops in the alloy a morphology comprised of gamma prime particles which consist essentially of randomly dispersed irregularly shaped particles less than about 0.35 micron in diameter.

The first stage of the heat treatment :is designed to put sufficient coarse gamma prime particles which form during alloy production, e.g., during casting and working, into solution. Particles begin to go into solution at a temperature of about 2,000 F. (give or take about 25 F. depending upon furnace accuracy) and solutioning is complete at about 2,l25 F. The

particular solutioning temperature employed depends upon the ultimate use for the alloys. For alloys to be used at service temperatures in excess of 1,800 F. it is preferable to use a solutioning temperature in excess of 2,125 F. as it is desirable to put substantially all the coarse gamma prime particles which do not contribute strength to the alloy into solution. For alloys to be used at a service temperature below 1,800 F. e.g., 1,400 F. it is sometimes desirable to use a partial solutioning temperature of from 2,000 P. to 2,125 F. as the lower solutioning temperature will produce an alloy with a finer grain size.

The second stage of the heat treatment is designed to initiate the formation of and form the randomly dispersed irregularly shaped fine gamma prime particles and to form a grain boundary precipitate, M C (M is generally chromium which improves grain boundary ductility. It is a time and temperature dependent process. At lower temperatures longer times are involved and at higher temperatures shorter times. A lower temperature limit of 1,500 F. is imposed as it would be commercially impractical to operate at lower temperatures when the time involved is considered. Ari upper temperature limit of 1,850 F. is imposed as M C begins to go into solution at this temperature and since the formation of cubic gamma prime particles is accelerated at higher temperatures. A preferred temperature range is from about 1,600 F. to about 1,800 F. No range can be placed upon the time period as it depends upon too many variables such as the temperature and the thickness of the material being treated.

The third stage of the heat treatment is preferable and not necessary. It is designed to precipitate additional M C particles and is performed at a temperature low enough to preclude detrimental gamma prime particle growth. The temperature range for this stage of the heat treatment is l,350l ,450 F.

The following examples are illustrative of the invention.

Several samples (Samples A, B, C, and D) were melted, heat treated, and photomicrographed. In addition, Samples A and B were tested for creep at 1,800 F. under a stress of 16 ksi. The samples had a composition consisting essentially of, in weight percent, 0.08% carbon, 16.9% cobalt, 15.1% chromium, 5.0% molybdenum, 3.47% titanium, 4.0% aluminum, 0.027% boron, balance essentially nickel with incidental impurities. Sample A was given a heat treatment which comprised the steps of: (lheating at a temperature of 2,135 F. for 4 hours and air cooling; (2) heating at a temperature of l,975 F. for 4 hours and air cooling; (3) heating at a temperature of 1,550 F. for 24 hours and air cooling; and (4) heating at a temperature of 1,400 F. for 16 hours and air cooling. Sample B was given a heat treatment which comprised the steps of: (l) heating at a temperature of 2,135 F. for 4 hours and air cooling; (2) heating at a temperature of 1,700 F. for 8 hours and air cooling; and (3) heating at a temperature of 1,400 F. for 16 hours and air cooling. Sample C was heat treated in the same manner as Sample B with the exception that the intermediate heating, i.e., the second stage heating, was at a temperature of l,750 F. Sample D was heat treated in the same manner as Sample B with the exception that the intermediate heating was at a temperature of l,750 F. for a 24-hour period.

The results of the creep tests for given A and B are shown in FIG. 1 wherein percent elongation is plotted versus time. A study of the results reveals that Sample B, which was given a heat treatment within the scope of this invention, had a lower second stage creep rate, i.e., the substantially constant creep rate commonly used for design purposes, than did Sample A which was given a conventional prior art heat treatment. Samples B and A had respective second stage creep rates of 0.006%/hour and 0.04%/hour. A part with a specification of 1% maximum creep at 1,800 F. under a stress of 16 ksi would have a useful life of about 10 hours with the conventional heat treatment given Sample A and a useful life of about 1 10 hours with the improved heat treatment given Sample B. Sample B, therefore, shows an 1 l to one improvement over Sample A.

Photomicrographs at 7,200X show the different morphologics of Samples A and B. FIG. 2, which is the photomicrograph of Sample A, is comprised of oriented cubic gamma prime particles about 0.5 micron per side (some of the gamma prime particles have a triangular or trapezoidal appearance due to the grain orientation and surface intersection) and FIG. 3, which is the photomicrograph of Sample B, is comprised of gamma prime particles which consist essentially of randomly dispersed irregularly shaped gamma particles which are less than about 0.25 micron in diameter. The photomicrographs clearly show that the lower second stage creep rate of Sample B is due to its particular morphology which results from the particular heat treatment of this invention.

The photomicrographs of FIGS. 4 and 5 show how the time and temperature of the second stage of the heat treatment of this invention affects the size of the gamma prime particles. Sample C, which was treated in the same manner as Sample B with the exception that the intermediate heating was at a temperature of 1,750 F. instead of 1,700 F. had gamma prime particles larger in size than the gamma prime particles of Sample B and Sample D which was treated in the same manner as Sample C with the exception that the intermediate heating was for 24 hours instead of 8 hours had gamma prime particles larger in size than the gamma prime particles of Sample C. Samples C and D are respectively shown at 7,200X in FIGS. 4 and 5.

Several additional samples (Samples E, F, G, and H) were melted, heat treated, and stress rupture tested at 1,650" F. under a stress of 35 ksi. The samples had a composition consisting essentially of, in weight percent, 0.05% carbon, 17.5% cobalt, 14.5% chromium, 4.5% molybdenum, 3.19% titanium, 4.20% aluminum, 0.028% boron, balance essentially nickel with incidental impurities. Sample E was given a heat treatment which comprised the steps of: (l) heating at a temperature of 2,l35 F. for 4 hours and air cooling; (2) heating at a temperature of 1,975 F. for 4 hours and air cooling; (3) heat ing at a temperature of 1,550 F. for 24 hours and air cooling; and (4) heating at a temperature of 1,400 F. for 16 hours and air cooling. Sample F was given a heat treatment which comprised the steps of: (l) heating at a temperature of 2,l35 F. for 4 hours and air cooling; (2) heating at a temperature of 1,700 F. for 4 hours and air cooling; and (3) heating at a temperature of 1,400 F. for 16 hours and air cooling. Samples G and 1-1 were heat treated in the same manner as Sample F with the exception that the intermediate heatings were for respective periods of 8 and 16 hours.

The results of the stress rupture tests for Samples E, F, G, and H are reproduced below in Table 11.

average ol'two specimens The data in Table 11 reveals that Samples F, G, and H, which were given heat treatments within the scope of this invention, had a longer life than did Sample E which was given a conventional prior art heat treatment. Sample G had an average life of 141.7 hours at 1,650 F. under a stress of 35 ksi with the heat treatment of this invention in comparison to an average life of 110.5 hours for Sample E which had a prior art heat treatment.

It will be apparent to those skilled in the art that the novel principles of the invention disclosed herein in connection with specific examples thereof will suggest various other modifications and applications of the same. It is accordingly desired that in construing the breadth of the appended claims they shall not be limited to the specific examples of the invention described herein.

lclaim:

l. A method of treating an alloy consisting essentially of, in weight percent, up to 0.18% carbon, from 14.2 to cobalt, from 13.7 to 16% chromium, from 3.8 to 5.5% molybdenum, from 2.75 to 3.75% titanium, from 3.75 to 4.75% aluminum, up to 4% iron, from 0.005 to 0.035% boron, up to 0.5% zirconium, up to 0.5% hafnium, up to 0.75% columbium, up to 0.5% rhenium, up to 0.75% tantalum, up to 1.0% manganese, up to 3% tungsten, up to 0.5% rare earth metals, balance essentially nickel with incidental impurities, to develop a morphology comprised of gamma prime particles which consist essentially of randomly dispersed irregularly shaped particles less than about 0.35 micron in diameter, which comprises the steps of: heating said alloy at a temperature of at least about 2,000 F. to put coarse gamma prime particles into solution, cooling said alloy, and heating said alloy at a temperature of from about l,500 F. to about 1,850 F. to initiate the formation of and form fine gamma prime particles.

2. A method according to claim 1 wherein said heating to put coarse gamma prime particles into solution is at a temperature of from about 2,000 F. to about 2,l F.

3. A method according to claim 1 wherein said heating to put coarse gamma prime particles into solution is at a temperature of at least about 2, 1 25 F.

4. A method according to claim 1 wherein said heating to initiate the formation of and form fine gamma prime particles is at a temperature of from about 1600F. to about 1800F.

5. A method according to claim 1 including the step of heating said alloy at a temperature of from about 1350F. to about 1450F. after said heating to initiate the formation of and form fine gamma prime particles.

6. A method according to claim 1 wherein said heating to put coarse gamma prime particles into solution is at a temperature of at least about 2125F. and wherein said heating to initiate the formation of and form fine gamma prime particles is at a temperature of from about l,600 F. to about 1,800 F 7. A method according to claim 6 including the step of heating said alloy at a temperature of from about 1,350 F. to about l,450 F. after said heating to initiate the formation of and form fine gamma prime particles. 

2. A method according to claim 1 wherein said heating to put coarse gamma prime particles into solution is at a temperature of from about 2,000* F. to about 2,125* F.
 3. A method according to claim 1 wherein said heating to put coarse gamma prime particles into solution is at a temperature of at least about 2,125* F.
 4. A method according to claim 1 wherein said heating to initiate the formation of and form fine gamma prime particles is at a temperature of from about 1600*F. to about 1800*F.
 5. A method according to claim 1 including the step of heating said alloy at a temperature of from about 1350*F. to about 1450*F. after said heating to initiate the formation of and form fine gamma prime particles.
 6. A method according to claim 1 wherein said heating to put coarse gamma prime particles into solution is at a temperature of at least about 2125* F. and wherein said heating to initiate the formation of and form fine gamma prime particles is at a temperature of from about 1,600* F. to about 1,800* F.
 7. A method according to claim 6 including the step of heating said alloy at a temperature of from about 1,350* F. to about 1, 450* F. after said heating to initiate the formation of and form fine gamma prime particles. 